Tri Phase Electric system - info on tariffs

We have an ancient 3-phase electric system. The main cable into our property was destroyed in a recent landslide and EDF are looking at alternative routes to our land. We had been considering switching to monophase at some point in the future, as the current arrangement of 15 amps per phase is not adequate. However, before making an irreversible decision, I want to investigate our future options if we keep to 3-phase.

I have looked at the various tariffs on the EDF site. But my question is: Does anyone know whether it is possible to increase the ampage on each phase of a 3-phase system in smaller increments, eg 3 x 20amps = 60 amps total? Or if we stick with 3-phase, would we have to double each phase from 15 to 30 making 90 amps in total (bit expensive and more than we need). Or is it possible to have different levels of amps on each phase?

Would really appreciate hearing back from anyone who has been in our situation.